Photometric in vitro determination of the content of an analyte in a biological sample has been disclosed in numerous publications. E.g. Austrian patent AT 382467 B relates to a sensor, a so-called optode, comprising a reaction chamber and an indicator chamber. On operation of the optode a sample is brought into contact with the optode and an analyte of the sample passes through a membrane of the reaction chamber and is converted therein to a reaction product which is subsequently measured in the indicator chamber. The analyte content is derived from the measurement of the reaction product. The reaction chamber may be provided as a membrane to which the reagent is bound.
There is also known a number of clinical chemistry analyzers which consist of a combination of disposable components, which are only used for one single analysis operation and only get in touch with one single sample, and an analysing section adapted for receiving the sample containing disposable device and containing the additional components necessary for accomplishing a clinical chemical analysis.
These analyzers all have in common that the transfer of blood sample from patient to disposable device takes place via a separate sampling device such as a syringe, a capillary tube or a vacuum tube sampling device.
In certain cases the sampling device and the disposable device constitute one and the same device. Thus, International patent application WO 86/00138 (Shanks et al.) discloses a device with a cavity sufficiently small for a given sample to be sucked into the cavity by capillary effect.
In this equipment the cavity is provided with an electrode structure and possibly a coating of a material adapted to the analysis to be performed with the equipment. The electrode structure provided in the cavity may i.a. be a potentiometric ion sensitive electrode structure or an amperometric electrode structure. The latter is described in connection with determination of hydrogen peroxide and oxygen in the sample.
Supplementary use of the equipment for optical analysis of the products of a specific binding reaction is also described.
From the specification of Danish patent publication DK 150804 (Lilja, J. E. and Nilsson, S. E. L.) is known a sample container for sampling, mixing a sample with at least one reagent and directly performing a separate optical analysis of the sample mixed with the reagent. The sample container has a capillary cavity coated with a reagent and the inlet to the sample container works by capillary effect. The sample container is stated to be useful for most different kinds of analysis and to be especially advantageous for determination of hemoglobin. A preferred embodiment of the sample container has deformable walls which may be compressed to a predetermined distance in the subsequent analysis procedure.
From the specification of British patent application GB 2025065 (Meiattini, F. et. al.) is known a plunger syringe for withdrawal of a blood sample. The blood sample is analysed by means of sensors incorporated in the syringe plunger. It is thereby avoided to transfer the sample to a sample station. The sensors are adapted for connection with an analyzer via conductors for registrating, processing, and outprinting analysis data. The specific sensors described in the specification of the said British patent application GB 2025065 are electrochemical sensors for blood gases and blood electrolytes.
None of the above-mentioned publications which in applicant's opinion represent the prior art closest to the present invention deal with the special problems connected with photometric determination of an analyte in whole blood.
A serious problem when performing a photometric analysis of a particular analyte in whole blood is that the light reduction caused by the remaining components in the sample is extensive as compared to the light reduction attributable to the analyte. Another serious problem is that due to its content of blood cells whole blood gives rise to a light reduction depending on the content of blood cells in the sample, i.e. of the sample hematocrit, and accordingly said light reduction will constitute an unknown factor. Varying content of other components than hematocrit may also result in a light reduction which varies between samples.